The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the electronics industry utilized light emitting diodes (LEDs) for various applications. Improvements in the LEDs improved the efficiency and increased the light emitting capabilities of the LEDs and led to increased applications. In some of the applications, several LEDs were connected together in series in order to provide a higher intensity light output. In such applications, if one of the LEDs failed in an open circuit condition, current could no longer flow to the remaining LEDs, thus, there was no light created by any of the LEDs. In some cases, a zener diode was connected in parallel with each LED to provide an alternate current path when the LED became an open circuit. The zener diode had a reverse voltage or zener voltage that was greater than the forward voltage of the LED so that the zener diode was not conducting current while the LED was operating, although some leakage current may have flowed through the zener diode. If the LED failed and became an open circuit, the zener diode became forward biased and began conducting the current that would be conducted by the LED. Because the zener diode had a higher voltage drop than the LED and conducted the same amount of current, the zener diode had to have a higher power dissipation capability than the LED in order to prevent damaging the zener diode. For example, an LED generally had a forward voltage of approximately 3 to 4 V. Consequently, the parallel connected zener diode had to have a reverse voltage that was greater than 3 to 4 V. Typically, the reverse voltage of the zener diode was much higher in order to minimize leakage current through the zener diode while the LED was operating normally. Thus, the zener diode generally had a reverse voltage of 6 to 8 V which required the zener diode to have a maximum rated power dissipation that was approximately twice the maximum rated power dissipation of the LED. The higher power dissipation generally increased the cost of the LED system. Additionally, the higher voltage drop across the zener diode limited the number of LEDs that could fail and still keep the remaining LEDs operating.
Accordingly, it is desirable to have a protection circuit that has an operating voltage drop that is no greater than the forward voltage of the LEDs, and that has a lower cost.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. For clarity of the drawings, doped regions of device structures are illustrated as having generally straight line edges and precise angular corners. However, those skilled in the art understand that due to the diffusion and activation of dopants the edges of doped regions generally may not be straight lines and the corners may not be precise angles.